Cardiac hypertrophy and congestive heart failure are significant causes of morbidity and mortality in the United States. The human heart undergoes hypertrophic growth in response to pathophysiologic stimuli such as chronic hypertension and valvular disease. The transition from normal to hypertrophied ventricle is marked by characteristic molecular phenotypic changes, including a switch in the energy metabolic gene regulatory program from predominantly fatty acid beta-oxidation (FAO) to the more oxygen-efficient glycolysis, a reactivation of fetal metabolism. Little is known about the hypertrophy signaling pathway linked extracellular stimulus to transcriptional regulation. The broad goals of this proposal are to delineate the molecular regulatory signals which ultimately contribute to down-regulation of FAO during hypertrophy. This proposal is specifically designed to i) characterize alterations in fatty acid beta-oxidation gene transcription in cultured rat neonatal cardiocytes undergoing hypertrophy and to delineate the specific cis-acting elements mediating that response utilizing Northern and Western blot analysis, RNase protection, and transient gene transfer studies with FAO enzyme gene promoters; ii) identify the specific transcriptional regulators that bind to the responsive elements in the promoters of beta-oxidation genes during cardiocyte hypertrophy utilizing electrophoretic mobility shift assay, cotransfection, Northern and Western blot analysis, RNase protection, and immunofluorescence; iii) determine whether the activity of the regulators are increased during hypertrophy by phosphorylation events utilizing in vitro and in vivo phosphorylation studies, inhibitors of known signal transduction cascades, and phosphorylation site mutations with emphasis on the mitogen-activated protein kinase pathway. The longterm goals will be to determine whether reactivation of this fetal metabolic gene program and/or downregulation of fatty acid beta-oxidation leads to a maladaptive hypertrophied phenotype and thus promotes the transition to heart failure. If so, the studies outlined above will have identified potential targets for therapeutic interventions aimed at delaying or even preventing progression to end-stage cardiomyopathy.